1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a thin film transistor substrate of polycrystalline silicon (poly-silicon) type and a fabricating method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for improving an aperture ratio without a deterioration in a capacitance value of a storage capacitor.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) has liquid crystal cells arranged in a matrix on a liquid crystal display panel to control light transmittance in accordance with video signals so as to display a picture. FIG. 1 is a plan view illustrating a related art thin film transistor substrate of amorphous silicon type. FIG. 2 is a cross-sectional view of the liquid crystal display panel taken along line I-I′ in FIG. 1.
Referring to FIG. 1 and FIG. 2, the liquid crystal cell includes a thin film transistor (TFT) 30 connected to a gate line 2 and a data line 4, and a pixel electrode 22 and a storage capacitor 60 connected to the TFT 30. The TFT 30 switches a video signal onto the pixel electrode 22. To this end, the TFT 30 has a gate electrode 6 connected to the gate line 2, a source electrode 8 connected to the data line 4, and a drain electrode 10 connected, via a pixel contact hole 20, to the pixel electrode 22. Further, the TFT 30 includes an active layer 14 overlapping the gate electrode 6 with a gate insulating film 12 therebetween and defining a channel between the source electrode 8 and the drain electrode 10. On the active layer 14, ohmic contact layers 16 make ohmic contacts with the source electrode 8 extending from the data line 4 and the drain electrode 10.
The storage capacitor 60 enables video signals charged on the pixel electrode 22 to be stably maintained. To this end, the storage capacitor 60 includes a storage line 52 provided in parallel to the gate line 2 to act as a lower storage electrode, and a pixel electrode 22 acting as an upper storage electrode. The pixel electrode 22 is provided in such a manner as to overlap the storage line 52 with the gate insulating film 12 and a protective film 18 therebetween.
The storage line 52 of the related art storage capacitor 60 is formed of an opaque metal in such a manner as to cross the pixel with a first width W1. A problem occurs in that the aperture ratio is reduced by an area of the pixel electrode covered by the storage line 52. On the other hand, another problem is raised if an area of the storage line 52 over the pixel electrode 22 is reduced to prevent a deterioration of aperture ratio, in that a capacitance value of the storage capacitor 60 is reduced.